Replies

1. 
   Farmersteve | Dec 23, 2004 03:11am | #1

   How thick are your laminations?

   I've bent maple to band the edges of a tabletop and found I had to cut them fairly thin and soak them to come out right.

    

                                                                                                Steve

1. 
   georgek | Dec 23, 2004 03:22am | #2

   The laminations are 4 plys at 3/16", I also tried 1/8" to the same results. I'm using yellow glue and letteng it set for 1 hour. Thank for responding!

2. 
   jmc | Dec 23, 2004 04:31am | #3

   It might be the glue. I've heard that yellow glue has more springback, and 1 hour probably isnt long enough anyway. I've used Unibond 800 with good results and I'm sure a urea resin would work. Hope this helps.

   John

3. 
   GHR | Dec 23, 2004 04:43am | #4

   You should have no springback from 4 3/16" laminations.

   Let the glue set for 24 hours before you remove the clamps.

4. 
   DennisS | Dec 23, 2004 05:28am | #5

   Benchdog -

   I'm not as experienced as others with respect to laminating bent wood, but with what little I've done I've bent to much tighter radii than what you describe with only minimal springback. First I agree, an hour isn't long enough for the glue to fully cure. Second I agree that ordinary yellow glue isn't my first choice for this application. I use the powdered resin glue which has far less 'creep'. Three laminations at 3/16" left in the clamps for at least 24 hours at proper temperature for the glue to cure should, in my (limited) experience be adequate to prevent all but the slightest springback.

   By the way, are you steam bending the laminations before you do the glue-up? I think it best to first get the material bent as close as possible to the final shape before laminating. Build yourself a bending form at somewhat tighter radius than the final form. Soak or steam the boards, clamp up in the form and allow 24 hours to cool and dry. Then glue them up.

   ...........
   From Beautiful Skagit Co. Wa.
   Dennis
1. 
   georgek | Dec 23, 2004 06:15am | #6

   Thank you everybody for responding, tomorrow morning I'll switch glue (polyurethane) and let it cure completely. Guess I'll have to make a few more cauls, deadline is Jan. 1! As far as steaming, I've never tried it before, probably not an option. As a last resort I'll bandsaw the pieces and clean up at the shaper, I just wanted to save some wood, this is Chicago, wood is at a premium.     Thanks again!                                   

1. 
   DougU | Dec 23, 2004 06:46am | #7

   benchdog

   I have done this numerous times, switch glue to the resin, don't waste your time trying to steam bend it, you wont gain enough to make it worth your time. I wouldnt bother to soak it either.

   Let the glue completely cure.

   4' radius is not that tight, you could try 1/8" laminates, couldn't hurt.

   Doug

1. 
   georgek | Dec 23, 2004 07:00am | #8

   Thanks Doug, I wouldn't dream of soaking it, I still have to stain it with analyne dye!  I haven't had any trouble before with cherry or mahogany, but this hard maple is a different animal!

5. 
   RickL | Dec 26, 2004 08:49pm | #9

   Not a very tough question. This formula was published on this site soem time ago and while not totally scientific it does work.

   "A number of plies of similar wood (n) are glued and clamped to a curved form, which is shaped to give the lamination a deflection of "x." When the clamps are removed, the lamination springs away from the form by an amount "y." Exactly how much springback can be predicted with the formula y = x/n2.

   The ratio of springback to the original deflection depends only on the number of laminations. The ratio does not depend on the properties or thickness of the wood or the geometry of the curved form. Thus, for two plies, the springback is one-quarter of the initial deflection, or one-ninth for three plies and one-sixteenth for four plies. "
   by Bill Clayden

   A glue with less creep and thinner laminations will result in less or no springback.

1. 
   georgek | Dec 26, 2004 08:59pm | #10

   Thank you, Rick, I'll use the formula tomorrow. I'll need to make some tighter cauls to compensate for spring-back and use a better glue.

1. 
   RickL | Dec 26, 2004 09:18pm | #11

   http://www.foremostwood.com/Cut%20Your%20Material.htm
   Here's another time and energy saver to try. Laminations are cut on a gang frame saw which yields pieces ready to glue, no sanding needed and minimal loss of kerf so a laminated piece doesn't look funny because of kerf loss. Send for a sample to see for yourself. I use a band clamp or vacuum press for what you are doing. The band clamp is a lot easier than a curved male and female form unless doing coumpound curves.

1. 
   georgek | Dec 26, 2004 09:51pm | #12

   Great site! Will use it in the future! Thanks.

1. 
   KeithNewton | Dec 27, 2004 01:52am | #13

   1/8" is what I would use with thickened epoxy, or urea. I did not find any mention of your glue surfaces. Are you jointing 1 face and sawing off the laminate then surfacing the other side, or are you using the saw kerf for the glue line?
   If your saw or jointer or planer knives are dull, you will have a lot of crushed cells which will spring back to some former memory, and keep the glue from getting to any undamaged cells.
   I always spread some of the glue onto a scrap of wood, and keep it near the glue up for quality control. You can test with your fingernail to determine whether there is enough set to avoid creep.
   Always make your parts longer than you need, you can not get the end of a laminate to bend any closer to the end than 8 times the thickness of the plys, thus 1/8" plys will have a 1" straight on each end. I try to make a practice of breaking or tearing up my scraps to see if the glue-line fails before the wood.

6. 
   Peter36 | Dec 27, 2004 04:18am | #14

   I have done laminations close to what you are saying and I would recommend 2 things. First is if you already have the cauls then get the wood in the correct curve before gluing. I have done this quite successfully on a hot wood stove pipe. Just hold the wood around the pipe and rub it back and forth forcing a bend in it. Secondly, if you are leaving the wood in its natural state then yes I would clamp to a tighter radius caul, or when doing it next time, make your radius whatever the plys return to after being unclamped.  Good luck, and how about posting some pics when its done.

1. 
   georgek | Dec 28, 2004 02:39am | #16

   Thanks Peter, I did just that. I let them sprinng back and used the new radius as a template. Nice trick! I took everyones suggestions and used resin glue and let it competely cure, no spring-back. Will post pics soon.

1. 
   Peter36 | Dec 28, 2004 03:37am | #17

   That trick saved my arse once. Glad it helped and we are all waiting for those pics!

7. 
   VomSorb | Dec 27, 2004 11:44pm | #15

   Thinner lams and DAP plastic resin glue will cure your problem.  I'd plane down to a weak eighth of an inch.